The invention generally relates to electronically commutated motors and controls therefor. In particular, the invention specifically relates to single phase motors, such as motors having external rotors for driving fans, and microprocessor controls therefor.
Motors with external rotors or "inside out motors" of the type to which the present invention generally relates have magnetic elements mounted on a rotor. These magnetic elements may include permanent magnets and/or electromagnets. A stator located inside the magnet elements includes a bearing for rotatably mounting a rotor shaft on the stator so that the rotor may rotate relative to the stator as a result of the magnetic interaction of the magnetic elements and magnetic fields generated by energizing windings of the stator.
In one embodiment, only one or two windings are wound on a bobbin of an inside out motor. Metal is provided around the bobbin, between the permanent magnets and the windings, to conduct the magnetic flux generated by the energized windings. Opposite ends of a plate are bent down so that the bent down ends may extend across the windings on diametrically opposite sides of the bobbin. The plate also has a central opening and a ring extending from the opening which is received into a central opening of the bobbin. Two substantially identical plates are mounted on axially opposite ends of the bobbin, and are angularly offset so that their bent down ends extend over different parts of the windings.
Such motors may be electronically commutated in order to provide variable speed operation or in order to allow operation at two or more distinct speeds. There is a need for a microprocessor control for such motors which is simple in design and low in cost to manufacture. In addition, there is a need for a control which has a reduced number of components as compared to single phase motors of the prior art and which can be programmed to operate in different modes without the need for changing components.